When operating oil and gas fields, oil recovery can be improved by injecting water within the deposit being operated, this via an injection well and in such a way as to push the oil of the deposit out of the ground, by at least one other well called a production well. The interaction of the injected water with the deposit containing the gas, the oil and groundwater can result in the formation of chemical species that may cause malfunctions of the installations. Barium sulphate deposits are particularly to be feared. Other types of deposits for example calcium carbonate or zinc and lead sulphides, can be formed in the presence of injection water as well as in the absence of it. The latter are in particular likely to be formed in operating conditions with high pressure and a high temperature or during the putting into contact of the brine that is injected in order to extract the oil or the gas with hydrogen sulphide or the ions contained in the deposit. The production of deposit or aquifer water simultaneously with the oil or gas can result in the same phenomena. These mineral deposits are able to obstruct the flow channels in the formation, pollute the duct and the surface equipment and block pumping systems and safety valves. More generally, mineral deposits or corrosion phenomena can appear in various operating conditions.
A common solution for eliminating these mineral deposits consisted in carrying out repeated acid washes. In addition to the problem of their short acting time, these treatments are not without risk for the equipment or for personnel, in particular in conditions of high pressure and high temperature.
To remedy this problem, it is possible to inhibit the formation of these deposits by continuous injection of inhibitors at the bottom of the well when the installations are in place. The so-called “squeeze” injection technique is an alternative to continuous injection.
The latter consists in the injection of a large quantity of product into the oil deposit while production is stopped. The deposit inhibitor once injected within the deposit must be adsorbed on the rock in order to be progressively released afterwards when production is resumed, this in order to prevent the formation of deposits over a long period of time, during the production of deposit water.
Molecular inhibitors of mineral deposits conventionally used in prior art as “squeeze” injection include phosphonates, vinyl sulphonate polymers (PVS), sulphonated polycarboxylic acids (SPCA) as well as polyphosphinocarboxylic acids (PPCA) which may be sulphonated (Kan and al. 2005, Journal of Colloid and Interface Science 281:275-284). These inhibitors are however considered to not be very heat stable, and some, such as phosphonates are troublesome for use due to the risks for the environment that they have. It has however been observed that conventional mineral deposit inhibitors were not effective for use in conditions of high pressure and high temperature. It has also been noted that polymeric inhibitors are not effective or are hardly effective for use as “squeeze” injection.
Chao and al (2013, OTC 24252) suggested using a formulation of inhibiting agents of the sulphonated polycarboxylic acid (SPCA) type coupled with alumina nanoparticles for “squeeze” injections. Zhang and al (2010, SPE 130639) have however also described silica-based nanoparticles comprising the Zinc-phosphonate association. Ghorbani and al (2012, SPE 156200) have moreover described the use of polyphosphinocarboxylic acid (PPCA) on a carbon-based nanoparticle. The synthesis of these nanoparticles is however difficult to implement and is costly, as each nanoparticle contains very little inhibitor with respect to the elements that structure nanoparticles proposed in prior art.
There is still therefore a need for a compound that makes it possible to inhibit or to slow done the formation of mineral deposits or of sulphides, which is stable at a high temperature and high pressure and/or that can be effective for a squeeze injection. It would furthermore be desirable for this compound to be able to be released in a prolonged manner, and for it to be simple to produce and/or inexpensive. Finally, it would be advantageous for these compounds to be biodegradable quickly and of low toxicity for the environment.
The inventors have demonstrated that these needs could be satisfied by using novel nanoparticles comprising
(i) a polyorganosiloxane (POS) matrix; possibly as coating of a lanthanide oxide core, and
(ii) at least one polymeric deposit inhibitor.